A 32-year-old woman from rural Odisha presents with fever, chills, and headache for 3 days. Blood smear shows P. vivax trophozoites. She is started on chloroquine 600 mg base stat, followed by 300 mg at 6, 24, and 48 hours. On day 12, she develops recurrent fever with P. vivax parasitemia. What is the most appropriate next step in management?

Explanation

## Clinical Context The patient has recurrent P. vivax parasitemia 12 days after completing a standard chloroquine course. This pattern is characteristic of **relapse**, not recrudescence, because P. vivax has a dormant hypnozoite stage in the liver. ## Why Primaquine Is Needed **Key Point:** Chloroquine kills only erythrocytic schizonts; it does NOT eliminate hepatic hypnozoites. Relapses occur when hypnozoites mature weeks to months later. **High-Yield:** Primaquine is the ONLY drug that eliminates hypnozoites (true causal prophylaxis). Standard dosing is 0.5 mg/kg/day for 14 days in non-severe G6PD deficiency; 45 mg weekly for 8 weeks in G6PD-deficient individuals. ## Mandatory G6PD Testing **Clinical Pearl:** Primaquine causes severe hemolysis in G6PD-deficient patients. In endemic regions (India, Africa, Mediterranean), G6PD screening is **mandatory** before primaquine initiation. **Warning:** Skipping G6PD testing and giving standard primaquine to a G6PD-deficient patient can cause life-threatening intravascular hemolysis. ## Management Algorithm ```mermaid flowchart TD A[P. vivax malaria diagnosed]:::outcome --> B[Give chloroquine 600 mg base stat,<br/>then 300 mg at 6, 24, 48 hrs]:::action B --> C{Fever resolves &<br/>parasites clear?}:::decision C -->|Yes| D[Test G6PD status]:::action C -->|No| E[Assess for chloroquine resistance<br/>or inadequate dosing]:::action D --> F{G6PD normal?}:::decision F -->|Yes| G[Primaquine 0.5 mg/kg/day × 14 days]:::action F -->|No| H[Primaquine 45 mg weekly × 8 weeks]:::action E --> I[Consider artemether-lumefantrine<br/>or artesunate-amodiaquine]:::action G --> J[Hypnozoites eliminated<br/>No relapse]:::outcome H --> J ``` ## Table: P. vivax vs P. falciparum Relapse/Recrudescence | Feature | P. vivax | P. falciparum | | --- | --- | --- | | Hypnozoites | Yes (dormant in liver) | No | | Relapse pattern | Common (weeks–months) | Does not occur | | Recrudescence | Rare | Common if inadequate treatment | | Chloroquine alone | Incomplete (relapses occur) | Adequate in sensitive strains | | Primaquine needed | **Yes** (mandatory) | No | ## Why Other Options Are Wrong - **Repeat chloroquine:** Will clear acute parasitemia again but will NOT prevent relapse because hypnozoites persist. - **Artemether-lumefantrine:** Effective for acute parasitemia but does not eliminate hypnozoites; relapse will recur. - **Increase chloroquine dose:** Chloroquine resistance in P. vivax is rare in India; the issue is hypnozoites, not drug resistance.